In order to facilitate the fullest possible participation by the Navajo Tribe in the program authorized by this subchapter, the members of the tribe shall have the right to adopt a tribal constitution in the manner herein prescribed. Such constitution may provide for the exercise by the Navajo Tribe of any powers vested in the tribe or any organ thereof by existing law, together with such additional powers as the members of the tribe may, with the approval of the Secretary of the Interior, deem proper to include therein. Such constitution shall be formulated by the Navajo Tribal Council at any regular meeting, distributed in printed form to the Navajo people for consideration, and adopted by secret ballot of the adult members of the Navajo Tribe in an election held under such regulations as the Secretary may prescribe, at which a majority of the qualified votes cast favor such adoption. The constitution shall authorize the fullest possible participation of the Navajos in the administration of their affairs as approved by the Secretary of the Interior and shall become effective when approved by the Secretary. The constitution may be amended from time to time in the same manner as herein provided for its adoption, and the Secretary of the Interior shall approve any amendment which in the opinion of the Secretary of the Interior advances the development of the Navajo people toward the fullest realization and exercise of the rights, privileges, duties, and responsibilities of American citizenship.